Processes for the preparation of oligosulphanes as such have been known for a long time.
In DE-PS 2141159 (U.S. Pat. No. 3,842,111), a process is described for the preparation of bis(alkoxysilylalkyl) oligosulphanes from the corresponding halogen alkylalkoxysilane and alkali metal oligosulphides, preferably in alcoholic solution. However, only mixtures of sulphanes with different chain lengths are obtained in this way.
According to a process described in DE-PS 2712866 (U.S. Pat. No. 4,129,585), an alkali metal alcoholate is reacted with a halogen alkylalkoxysilane, metal or ammonium hydrogen sulphide and sulphur in the presence of an organic solvent. The preparation of the alkali metal alcoholate solution is very time-consuming, however, which makes industrial-scale implementation of the process unlikely.
A process is known from U.S. Pat. No. 5,466,848 in which hydrogen sulphide is reacted with an alkoxide, the reaction product is treated with elemental sulphur, and then reacted with a halogen alkylalkoxysilane to obtain the desired organosilicon polysulphane.
Similarly, according to U.S. Pat. No. 5,489,701, operations are carried out with alkoxides and hydrogen sulphide, a compound which is known to be very unpleasant to handle. The reaction of anhydrous sodium sulphide and sulphur with halogen alkoxysilanes is described in the specification of JP 7-228588.
A mixture of polysulphanes is obtained in this way, as tests showed.
Organosilicon polysulphanes, particularly bis(triethoxysilylpropyl)tetrasulphane in combination with highly reactive silica fillers, are used in the preparation of vulcanised rubber articles, particularly tires.
The advantageous use of high-purity disulphanes with regard to the processing and properties of vulcanizates is described in EP-A 0732 362 (U.S. Pat. No. 5,580,919) and in Panzer (L. Panzer, American Chem. Soc., Rubber Div. Meeting 1997).